Typical coin operated telephone units include a mechanism for retaining deposited coins until receipt of a control signal from the central office (CO). As is known to those skilled in the art, the coin mechanism used in coin operated telephone units includes a coin relay, having a resistance of 1020 ohms, for example, a coin sensor and a totalizer. The totalizer closes a switch between the tip line and a circuit including a series connection between a further switch contact operated by the coin sensor and the coin relay. The coin sensor closes the further switch contact upon sensing deposit of a coin. Before the totalizer allows the coin ground to be placed on the tip line, however, the amount of currency represented by the deposited coins must meet or exceed a predetermined "initial rate".
Thus, upon deposit of a coin, both the totalizer and coin sensor operated contacts are closed, completing a circuit between the coin relay and the tip line. The polarity of a 130 V voltage placed on the tip line by the CO determines whether the coin relay energizes a gate mechanism in a coin chute for directing a coin held therein to be collected or to be returned.
In operation, the coin relay generates two conditions of electromagnetic flux. A first condition is generated when the relay is connected to the voltage from the CO, and a second condition is generated when the relay is released from the CO. The first and second conditions correspond to expansion and collapse of the flux generated by the activated relay. However, the flux conditions may similarly refer to first and second flux levels generated by the relay in response to reception of a voltage of a particular polarity from the CO.
The time period between the two flux conditions, particularly between the expansion and collapse of flux generated by the relay coil, is required to be within predetermined limits for proper operation. More particularly, the time between energization and collapse must be sufficiently long to permit all coins to be collected before a gate in the coin chute is closed. If the time is too short, the gate closes too soon and coins may become stuck in the chute.
However, if the time is too long, excessive power is used and the timing specifications of various Electronic Switching Systems may be affected. That is, the CO equipment can only stay on line for no more than a preset period of time to cause return or collection of a coin, since the equipment is charged with performing numerous other tasks. Coin relays in coin operated telephones are thus provided with an adjustment apparatus, typically in the form of an adjustment screw, for adjusting the timing thereof.
Accordingly, it is necessary to maintain the timing of a coin relay within predetermined limits. Thus, proper operation of a relay may be detected by detecting the timing between the two flux conditions generated thereby, and particularly between the expansion and collapse times for the flux fields generated thereby.
In order to test the coin relays for proper operation, a known technique relies on repair personnel accessing the CO via a test trunk, dialing a particular three digit number to conduct the coin relay test, depositing a coin and waiting for the CO to generate a predetermined number of beeps after the test circuit returns the coin.
Responsively to the dialed test code, the CO senses minute current flow to confirm the initial coin deposit. When the coin needs to be collected or returned, a 130 V voltage is applied to the tip line, at positive or negative levels to energize the relay for collecting or returning the coin.
However, only one test trunk is typically available for each CO. Thus, if a number of repair personnel are in the field, long delays may be experienced by each repair person attempting to access the test trunk if other personnel are simultaneously attempting to access the same trunk. Such delays may result in various coin operated units remaining untested, in additional time and thus expenses for repair and maintenance, and in loss of revenue from inoperative and uncorrected coin units.
Although a number of prior art methods are known for testing coils, such methods suffer from the above described deficiencies. Thus, in Stokes U.S. Pat. No. 3,496,300 assigned to Bell Telephone Laboratories, Inc., there is described a method for remote testing of a coin relay of a coin telephone by applying particular signals to the ring and tip leads to activate various contacts of a tuned reed relay. The voltage levels on the ring and tip leads are then monitored to determine proper operation of the coin relay, as well as other aspects of a coin telephone.
Other prior art tests for relays are generally known, including application of flux by calibrated coils and counting of pulses generated by movement of a reed switch blade. Alternatively, flux is applied to a relay and the quantity of flux needed to activate a reed switch is noted. In still another approach, a coil in the relay supply line detects the counterelectromotive-force caused by movement of a relay activated arm. The coil pulses a transistor to enable passage of a control signal, thereby controlling timing of controls.
However, none of the prior art addresses or solves a problem of locally determining the operational condition of a coin relay in a coin telephone, without accessing voltages on tip and ring lines and without accessing a test trunk of the CO.
There is thus a need in the prior art for a method and apparatus for testing coin relays without incurring the presently experienced delays in accessing a test trunk of a central office.
There is a more particular need in the prior art to eliminate the requirement for accessing the test trunk of the CO merely to test the operating condition of a coin relay.